Fluorene type compounds as organic photoconductors

ABSTRACT

An organic photoconductor which is the compound fluorene and derivatives in which fluorene is fused with benzo and naphtho ring structures. The dibenzofluorenes and fluorenes are dispersed in suitable resin binders over the range of 1-100 parts by weight to 10 parts binder and applied to a conductive substrate.

United States Patent Inventor FLUORENE TYPE COMPOUNDS AS ORGANIC IPHOTOCONDUCTORS 10 Claims, No Drawings 1.1.8. Cl 96/1.5, 96/1 R, 252/501 Int. Cl G03g 13/22, 603g 5/06 Field of Search 96/1.5, 1;

[ 56] References Cited UNITED STATES PATENTS 3,155,503 11/1964 Cassiers et a1. 3,245,783 4/1966 Neugebauer eta1.. 3,252,794 5/1966 Schaum et a1. 3,257,204 6/1966 Sus 3,287,123 11/1966 l-loegl 3,301,676 1/1967 Tomanek 3,307,940 3/1967 Hoegl Primary Examiner-Ge0rge F. Lesmes Assistant Examiner-John C. Cooper, 111 Att0rneySo1 L. Goldstein ABSTRACT: An organic photoconductor which is the compound fluorene and derivatives in which fluorene is fused with benzo and naphtho ring structures. The dibenzofluorenes and fluorenes are dispersed in suitable resin binders over the range of 1-100 parts by weight to 10 parts binder and applied to a conductive substrate.

FLUORENE TYPE COMPOUNDS AS ORGANIC PHOTOCONDUCTORS BACKGROUND OF THE INVENTION pattern of light and shadow producing a charge pattern cor- 1O responding to the image portions of the original desired to be reproduced. This image is then developed by applying electrostatically attractable powder, generally known in this art as toner.

The photoconductive medium usually comprises a conductive support to which has been applied a photoconductive layer of film, such as selenium, zinc oxide, or an organic material, such as anthracene. In the case of zinc oxide, which is an inorganic photoconductive crystalline material, the photoconductor is dispersed in a resin binder. Similarly, organic photoconductive materials can be dispersed in a film forming binder and applied to the conductive support.

SUMMARY OF THE INVENTION in which R is a fused arenic ring structure having eight carbon atoms and R is a fused arenic ring structure having from four to eight carbon atoms and x and y represent hydrogen, halogen, lower alkyl and lower alkoxy.

The base support on which the organic photoconductive layer is applied may be paper which has been treated to render it conductive, or it can be metal or a metal foil such as aluminum, copper, or zinc The use of a polyester film which has been metallized has given excellent results as a conductive support because it is dimensionally stable and at the same time possess all the advantages of a sheet of paper. It is essential that the support have a conductivity in the range of from mhos/centimeters to the conductivity level of metal It is the general object of the present invention to provide an improved organic photoconductive medium comprised of benzo and naphtho derivatives of fluorene.

It is another object of this invention to provide an organic photoconductive layer which is formed by dispersing an organic photoconductive material in a resin binder. It is sill another object of this invention to provide an organic photoconductive material comprising benzo and naphtho derivatives of fluorene dispersed in the resin binder system which has been sensitized to extend its spectral response into the visible range of the spectrum.

DESCRIPTION OF THE INVENTION Typical of the photoconductive materials useful in the preparation of the photoconductive members having the above general formula which are to be used in accordance with this invention are as follows:

dibenzofluorene 1'1,

O 2,3, benzofluorene 1,2:6,6 dibenzofluorene 3,4, benzofluorene H, C) 1,2:7,8 dibenzofluorene 6 2,5 dimethyl-7H- benzo [c] fluorcne O -CH;

CHaO

J-othyl-lllL benzo [a] H; 0 Iluorenc Cl- C The preparation of these compounds is well known and has been described in the literature, The Chemistry of Carbon Compounds, Volume II, by Victor Von Richter, Edited by Richard Anschutz, translated by MJ. Mee, Elsevier Publishing Company, 1946, pages 683 and 684.

1,2 Benzofluorene is obtained by reduction of 1,2 Benzofluorenone (Graebe, Ann. 335,134) or by passing the vapor of benzylnaphthalene through a red hot tube (Graebe, Berichte 27,953).

2,3 Benzofluorene is obtained by reducing 1,2 Benzofluorenone which is obtained by condensation of a hydroquinone with phthalaldehyde.

3,4 Benzofluorene is obtained by decarboxylating 3,4 benzofluorenone-l-carboxylic acid, which is obtained from the anhydride of l-phenyl-naphthalene-2,3-dicarboxylic acid by treatment with aluminum chloride.

To prepare the photoconductive members of this invention the photoconductive material is dispersed in a resin binder over the range of 1 to 100 parts by weight of the photoconductive material to parts by weight of the resin binder.

A wide range of materials may be use as the polymeric binder such as polyvinylchloride, polyvinylacetate, polyvinylacetals, polyvinylethers, polyacrylic and polymethacrylicesters, polystyrene, chlorinated rubber, alkyd resins, phenol formaldehyde resins, styrenebutadiene copolymers, polyamide resins and admixtures thereof, The preferred resin binder is a styrenebutadiene copolymer sold under the trade name of PLIOLITE manufactured by Goodyear Tire and Rubber Company.

The photoconductive material is dispersed in the resin binder such as styrenebutadiene copolymer by cold mixing and applied to a suitable base support in the form of a uniform continuous layer by conventional coating means, such as a wire-wound rod or trailing blade coater at the rate of 0.5 grams to 4.0 grams per square foot, preferably 0.75 grams to 1.0 grams to produce a film thickness in the range of 0.1 mil to 3.0 mils, pr preferably in the range of 1.0 mil to 1.5 mils. The coating is passed through a drying over in order to force evaporate the excess solvent.

The photosensitivity of the photoconductive materials prepared by the foregoing general procedure is in the ultraviolet portion the spectrum. It is desirable to extend the photosensitivity of the materials to the visible range of the spectrum in order to make possible the use of ordinary tungsten'type filament sources which emit radiation over the range of from 360 millimicrons to 725 millimicrons. The extension of the photosensitivity is known to be accomplished by the addition of small amounts of sensitizers, which may be chemical sensitizers, such as rr-type acids or dyesensitizers of the type disclosed in US. Pat. No. 3,052,540. A list of 90 -type acids which may be used as sensitizers is provided below which is by no means exhaustive and merely exemplary of the type of materials that may be used. The amount of sensitizers employed may range anywhere from 0.01 percent to 100 percent by weight based on the weight of the photoconductive material, the preferred range being between 10 percent 50 percent by weight of the photoconductive material.

CHEMICAL SENSITIZERS a. Anhydrides;

1. Tetrachlorophthalic anhydride 2. Naphthalene-1,4,5,8-tetracarboxylic hydride b. Cyanocarbons l. Tetracyanoethylene 2. 7,7,8,8-tetracyanoquinodimethane c. Quinones:

l. Chloranil 2 2,3-dichlorodicyano-l,4-benzoquinone 3. Phenanthrenequinone d. Nitroaromatics:

1. 1,3 ,S-trinitrobenzene 2. 9, l 0-dibromoanthracene 3. 2,4,7-trinitrofluorenone 4. 2,4,7 -trinitromalonodinitrile A wide variety of sensitizing dyes may be used to extend the response to include the visible range of the spectrum as such as are disclosed in US. Pat. No. 3.05 2,540, the preferred dyes being selected from the xanthene group and in particular the fluorescein and phloxene dyestuffs.

The process of making a reproduction utilizing the photoelectrostatic members of this invention involves applying a sensitizing electrostatic charge to the photoconductive layer in the range of from 200 volts to 2000 volts by means of a corona discharge electrode which is connected to a high potential source of from 4000 to 7000 volts. It will be appreciated that other means of applying electrostatic charge may be employed such as disclosed in US. Pat. application Ser. No. 760,027, filed Sept. 16, 1968, in the name of James A Fortcamp and assigned to the same assignee as the instant application. The materials may be charged either positively or negatively. The charge layer, upon receiving photoelectrostatic charges in the dark, becomes sensitive to electromagnetic radiation and is then exposed to a pattern of light and shadow by directing the radiation through a light transmitting original which is placed in contact over the photoconductive layer or by illuminating the graphic original with suitable radiation and then projecting the reflective pattern through a lens system onto the photoconductive member.

In general the charged electrophotographic member may be imaged by such other techniques as the use of a controlled laser beam which can depart to the surface a suitable image to be reproduced.

acid dian- Exposing the photoconductive layer to such a pattern of light and shadow or beam writing, produces a corresponding electrostatic image with a charged area corresponding to the shadow or unexposed portions and in the light struck areas the charge is dissipated through the conductive support.

A charge image is rendered visible by the application of a suitable toner which adheres to the image portions. Positively oriented toners are generally employed where the sensitizing charge is negative and reversal oriented toners are used for positively charged members, both systems producing a positive print from a positive original. The makeup of these toners is well known in the art and need not be further described here.

The material image is then fixed directly on the member or it may be transferred under controlled conditions to a receivable sheet, such as plain paper, and then fixed. The transferred material image may be fixed by exposing the toner to a source of heat which causes the material to coalesce and fuse to the support. In the circumstance that the toners are pressure responsive, they can be fixed by pressure, such as passing the members between a set of pressure rollers.

Paper base materials provided with a continuous thin film of uniform thickness of the photoconductive substances according to the present invention were eminently successful as photoelectrostatic members which became the final copy upon the fixing of the powdered image thereon. The application of the photoconductive material to metallized films gave excellent results as a reusable photoconductive medium suitable in a reproduction process such as described in LJ.Sv Pat. application Ser. No. 632,819, filed Oct. 3. 1967, now abandoned and assigned to the same assignee In the circumstance that transparent supports are used, the photoelectrostatic members can be used to effect reflex-type exposures 111 which a two-sided graphic original is exposed directing the radiation through the photoelectrostatic member to impinge upon the graphic subject matter reflexing a pattern of light and shadow onto the photoconductive layer. The following examples are presented for illustrating the present invention without limiting the scope thereof EXAMPLE I A photoelectrostatic member was prepared by dlspersing grams of 2,3 Benzofluorene in 90 grams of a styrene-butadiene copolymer sold by Goodyear Tire & Rubber Company. under their trade name PLIOLITE S-SO which was dissolved in 360 grams of toluene (a percent by weight resin solution).

To the dispersion was added 0.84 grams of a 1r-type acid 2,4,7-trinitrofluorenone malonodinitrile which represents 8.4 percent by weight sensitizer based on the weight of organic photoconductive material. The solution was placed in a ball mill and ball milled for a period of 24 hours until the crystals of 2,3 Benzofluorene and the ir-type sensitizer were uniformly dispersed in the resin binder solution The dispersion was removed from the ball mill and applied to an aluminized terephthalate film at a rate sufficient to lay down a coating weight of 2 grams per square foot of base support.

The aluminized mylar web was then passed through a heated forced air drying oven and the excess solvent evaporated resulting in a final coating thickness on a dry basis of 1 mil.

EXAMPLE II The photoelectrostatic member of this example was prepared by adding grams of 2,3 Benzofluorene to 45 grams of styrene-butadiene dissolved in 405 grams of toluene (10 percent copolymer solution by weight) and 7.56 grams of a chemical sensitizer 2,4,7-trinitrofluorenone malonodinitrile which represents 16.8 weight percent sensitizer based on the weight of 2,3 Benzofluorene.

The dispersion was mixed in a ball mill for a period of 24 hours and then applied to a conductive base support such as an aluminized mylar film at a rate of 2 grams per square foot of base which produced a thickness of 1 mil on a dry basis after having removed all excess solvent by passing the film through a forced hot-air ovenv EXAMPLE III A photoelectrostatic member was prepared by dispersing 100 grams of 2,3 Benzofluorene m 10 grams of styrene-butadiene copolymer dissolved in 490 grams of toluene (2 percent copolymer solution by weight) The mixture was charged into a ball mill to which was added 84 grams of the chemical sensitizer 2,4,7 trinitrofluorenone malondinitrile which represents 84 percent by weight concentration of sensitizer based on the weight of photoconductor The dispersion was ball milled for a period of 24 hours and then applied to a paper base support having a conductivity of 10 mhos per centimeter, and a caliper of 24 mils. The coating was applied at a rate sufficient to produce a photoconductive layer of 2 grams per square foot having a thickness of about 0.75 mils.

EXAMPLES IV-VI The photoelectrostatic members prepared in the instant examples followed the procedures described in connection with examples I, I1, and III with the exception that there was substituted for the photoconductive material of each formula the compound 3,4 Benzofluorene EXAMPLES VII-IX The photoelectrostatic member of these examples was prepared in the same manner as described in examples I, II and III, respectively with the exception that there was substituted for the photoconductive material in each formula the compound 1,2 Benzofluorene EXAMPLES I-XII ple. The dye stuff imparted a purple color to the photoconductive layer.

EXAMPLES XIII XV The photoelectrostatic members prepared according to these examples follows the preparations of examples I, II and III, respectively with the exceptlon that there was substituted for the resin binder in each case polyvinylbutyral sold under the trade name BUTVAR B-76 EXAMPLES xvi -IXX The photoelectrostatic members of these examples followed the preparation of examples I, II and III, respectively, with the exception that there was substituted for the resin hinder the material polyvinylformal, a resin manufactured by the Poly Sciences, Inc. of Rydal, Pennsylvania.

EXAMPLE XX The photoelectrostatic member of this example was prepared following the procedures of example II with the exception that fluorene was substituted for the 2,3 benzofluorene ad 45 grams of 2,4,7-trinitrofluorenone malonodinitrile was added which represents 100 weight percent sensitizer based on the weight ofthe fluorene.

The production of images on the photoelectrostatic members prepared in the above examples I-XX was accomplished by applying a sensitizing charge by means of a corona discharge electrode. The layers were charged to about 800 volts and then exposed to a pattern of light and shadow requiring an exposure in the range of to foot candle seconds using a tungsten radiant energy source. Development was in the conventional manner using cascade or magnetic brush to apply the electroscopic powder The class of organic photoconductive materials described herein can be used with base supports which in themselves form the copy material such as a paper base support, or the medium can be reused to produce high quality reproductions by transfer to plain paper.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof.

What is claimed is:

1. A photoelectrostatit recording element comprising a conductive base having applied thereon a photoconductive layer which includes a photoconductive material having the general formula:

where R is a fused arenic ring structure having eight carbon atoms and R is a fused arenic ring structure having four or eight carbon atoms, and x and 1 represent hydrogen, halogen, lower alkyl and lower alkoxy, said photoconductive material being dispersed in a film forming resin binder.

2. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 2,3, Benzofluorene.

3. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 1,2 Benzofluorene.

4 The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 3,4, Benzofluorene.

5. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 2,3:6,7 dibenzofluorene.

6. The photoelectrostatic member as claimed in claim 1 wherein said photoconductor material is 1,2:5,6 dibenzofluorene.

7 The photoelectrostatic member as claimed in claim 1 wherein said photoconductrve material is l,2:7,8 fluorene- 8 A photo reproduction process which comprises exposing an electrostatically charged photoconductive layer adhered on a conductive base support to a pattern of light and shadow and developing the resulting charge image with a developer material, the photoconductive layer comprising a compound having the general formula:

wherein said photoconductive material is -isopropyl-llH- benzo fluorene. 

2. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 2,3, Benzofluorene.
 3. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 1,2 Benzofluorene.
 4. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 3,4, Benzofluorene.
 5. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 2,3:6,7 dibenzofluorene.
 6. The photoelectrostatic member as claimed in claim 1 wherein said photoconductor material is 1,2:5,6 dibenzofluorene.
 7. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 1,2:7,8 dibenzofluorene.
 8. A photo reproduction process which comprises exposing an electrostatically charged photoconductive layer adhered on a conductive base support to a pattern of light and shadow and developing the resulting charge image with a developer material, the photoconductive layer comprising a compound having the general formula: where R1 is a fused arenic ring structure having eight carbon atoms and R2 is a fused arenic ring structure having four or eight carbon atoms and x and Y represent hydrogen, halogen, lower alkyl and lower alkoxy, said photoconductive material being dispersed in a film forming resin bInder.
 9. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 1,2,7,10-tetramethoxy-11H, benzo fluorene.
 10. The photoelectrostatic member as claimed in claim 1 wherein said photoconductive material is 6-isopropyl-11H-benzo fluorene. 